GEOC 86 |
| Pavan K. Naicker1, Vishal N Koparde1, Peter T. Cummings1, and Ariel A. Chialvo2. (1) Department of Chemical Engineering, Vanderbilt University, VU Station B 351604, Nashville, TN 37235, (2) Chemical Sciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Bldg. 4500-S, Mail Stop 6110, Oak Ridge, TN 37831-6110 |
| In this work the properties of isolated titanium dioxide nanoparticles are examined by molecular dynamics simulation. Simulations of nanoparticles in the three commonly occurring phases (anatase, brookite and rutile) were carried out. From this, the structural properties of the nanoparticles were investigated. The structural properties were inferred by simulated X-ray diffraction patterns and were compared to bulk phase x-ray diffraction patterns in order to understand the effect of size on the structural properties of titanium dioxide nanoparticles. The simulations indicate that for small particles the stable phase at low temperatures is anatase in contrast to the bulk phase where rutile is the most stable phase. During the course of the simulation (measured in nanoseconds) the isolated nanoparticles did not spontaneously change phase from the less stable rutile to the more stable anatase phase. This is attributed to the high activation energy barrier for the phase transformation of isolated nanoparticles. The titanium – oxygen bond length is dependant on the coordination environment of the titanium. The bond length is shorter when the titanium is surrounded by four oxygen ions and is longest when the titanium is surrounded by six oxygen ions. Smaller nanoparticles are characterized by a higher fraction of titanium ions that are 4 and 5 coordinated. The fusion and attachment of titanium dioxide nanoparticles were investigated. At high temperatures fusion is a rapid process and was successfully captured by the simulation. At low temperatures only the attachment of the nanoparticles were observed during the course of the simulations. In these simulations the fusion of two particles of the same phase produced a larger particle of the same phase whilst the simulation of a 3nm rutile and a 3nm anatase particle produced a larger rutile particle. |
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Interfacial Phenomena: Linking Atomistic and Macroscopic Properties
1:00 PM-5:50 PM, Tuesday, March 30, 2004 Marriott -- Marquis NW, Oral
Division of Geochemistry |